1. Field of the Invention
The present invention relates to a latch needle for loop forming textile machines. The needle includes a steel needle shank that is equipped with a needle hook at one end of the shank and a sawslot defined in the needle shank. The needle also includes a latch pivotally mounted in the sawslot so that it is pivotal about a transversely extending axle. The latch is pivotal between an open position and a closed position. In the closed position, the noucat (also called the latch spoon) rests on the needle hook and in the fully open position, the back surface of the latch rests on contact surfaces in the region of the upper edge of the needle shank.
In high speed loop forming textile machines, such as circular knitting machines, the latches of the latch needles are subjected to very high stresses. Because these latch needles are currently oscillated between the closed position and the fully open position at a frequency of 60 Hz or more, high acceleration and deceleration forces act on the latch. These forces not only subject the latch to bending stresses but also force the contact surfaces provided on the needle shank to absorb energy when the noucat impacts the hook or the back of the latch impacts on the shank. This energy must be absorbed by the shank or hook by elastic bending deformation and must be dissipated by friction. As a consequence of these high stresses exerted on the needle, not only may the noucat and the hook be damaged, but the latch may break and the latch bearing and/or the needle shank may be damaged.
2. Discussion of the Prior Art
Various different solutions have been proposed in the prior art to avoid the possible damage described above. For example, German Pat. No. 2,714,607 (to which corresponds U.S. Pat. No. 4,294,086) discloses a special configuration of the needle sawslot to elastically absorb the impact of the latch in the fully open or standing position. However, while this is an effective measure for absorbing the impact of the back of the latch as it contacts the shank, it is unable to influence or reduce the undamped impact of the latch noucat on the needle hook.
German Pat. No. 3,331,031 (to which corresponds U.S. Pat. No. 4,601,180) discloses a latch needle where the latch has at least one continuous recess in the region between the bearing bore and the noucat. This results in a reduction of mass which reduces the acceleration and deceleration forces generated by the pivoting movement of the latch. This also reduces the impact energy of the noucat on the needle hook as well as the impact energy of the back of the latch on the respective contact surfaces of the needle shank. However, due to the minute dimensions involved in latches for very fine or thin needles, the making of these recesses involves considerable expense.
German Pat. No. 1,046,819 discloses a latch needle that is particularly adapted for home (manual) knitting machines. The latch is made of a non-magnetizable material such as beryllium bronze or a synthetic compressed substance. This reference claims that by using a non-magnetizable material for part of the needle head and particularly for the latch, the latch will not stick to the hook as a result of remanent magnetism. The problem of the latch sticking to the hook due to magnetism occasionally occurred in latch needles made uniformly of magnetizable steel and utilized in home knitting machines. However, this problem does not occur in latch needles used in industrial machines. Moreover, latches made of beryllium bronze or of a compressed substance are unable to withstand the long-term stresses that they are subjected to in high speed circular knitting machines.